Basking Sharks: Satellite Tags Reveal Key Habitats For Conservation

The Sea of the Hebrides off the west coast of Scotland may be an important feeding area and migratory corridor for basking sharks, a recent three-year satellite tagging project revealed.

During the summers of 2012, 2013 and 2014 nearly 61 basking sharks were tagged by researchers from the University of Exeter and the Scottish Natural Heritage (SNH) as part of the Basking Shark Satellite Tagging Project. Researchers found the sharks regularly returned to the Sea of the Hebrides and spent most of their summer in this area, according to a new release.

Basking sharks are the world's second biggest fish and can grow up to 36 feet in length and weigh up to seven tons. Since the sharks don't have teeth, they feed on microscopic plankton by scooping them up in their remarkably large mouths. The sharks were fitted with satellite tags near the islands of Hyskier, Coll and Tiree, which are surrounded by waters rich with plankton for feeding on.

"It's been really exciting to learn that the same individual basking sharks return in consecutive years to use Scottish waters. It's something we thought happened -- but we now have the first proof that this occurs," Dr. Suzanne Henderson, project manager from the SNH, explained in the release. "It really does emphasize that the Sea of the Hebrides is highly important for this migrating species."

In autumn, tagged sharks dispersed widely from shallow waters around the Scottish islands towards deeper waters to the west of Ireland, the Bay of Biscay, Iberian Peninsula and North Africa. This travel pattern suggests the area represents an important migration corridor for basking sharks moving between the Sea of the Hebrides, the Isle of Man and southwest England.

"As well as cruising around and feeding at the surface the sharks can be seen showing courtship-like behaviors, such as jumping clear of the water, known as breaching and swimming around nose-to-tail," Dr. Henderson added. "These social behaviors suggest that the sharks return to the area not just to feed on the plankton bloom but for other reasons too, perhaps even to find a mate."

Identifying and managing areas where the sharks gather to feed or mate plays a key role in their conservation. Therefore, researchers have recommended that an area of the Sea of the Hebrides be designated as a marine protected area (MPA) for migratory basking sharks.

The satellite tags also shed light on how deep the sharks are able to dive: During the winter months researchers found seven of the the tagged sharks dove to depths greater than 1000 meters below the surface.

"It's been a truly exciting project with many highlights and challenges along the way. It has improved our understanding of the life history of basking sharks and confirmed that the Sea of the Hebrides is a special place for these captivating fish," Dr. Matthew Witt from the University of Exeter, added. "We hope our combined efforts yield a more secure future for basking sharks in coastal and offshore waters and that the impact of the project reaches far, influencing marine spatial planning policy, public engagement and the global conservation agenda."